The purpose of this Mentored Research Scientist Development Award (K01) is to help me become an independent researcher focused on identifying modifiable structural factors that can explain and address disparities in substance use and sexual risk behaviors, and thus rates of HIV acquisition, among young men who have sex with men (YMSM) in the U.S. The training from this K01 will allow me to 1) apply my qualitative skills to policy case study analysis; 2) learn and apply key quantitative methods (i.e. structural equation modeling and longitudinal data analysis) to analyze population-based data and the impact of structural interventions; 3) understand the multi-level factors that influence substance use and sexual risk for YMSM; and 4) gain skills in public health ethics relevant to substance use, HIV and YMSM. My career development plan includes specific seminars, workshops, coursework, conferences, hands-on practica and tailored mentoring with a mentorship team comprised of experts in structural HIV prevention, HIV risk for YMSM, substance use- and sexual health- focused policies, quantitative methods and public health policy analysis. The focus on YMSM is particularly important as they are at nearly twice the risk of substance use compared to their heterosexual peers. In 2013 YMSM constituted 92% of new HIV infections among young men; indeed, YMSM are the group for whom HIV incidence is increasing most rapidly. The majority of YMSM-focused HIV interventions have targeted individual- level factors; little is known about how structural factors influence HIV risk for YMSM To achieve the combination HIV prevention approach outlined in the US National HIV/AIDS Strategy, and a goal of NIDA, it is important to identify modifiable structural-level factors (e.g. state-level policies) that can be intervened upon to address HIV risk for YMSM on a population level. However, no published studies have examined how the state-level policy climate-i.e., the aggregate impact of public health policies-affects HIV risk for YMSM. To fill this gap, the proposed research will first examine whether the state-level policy climate explains differences in substance use and sexual risk for YMSM across the US. It will then use longitudinal data analysis and policy case study analysis to assess how a state's political context influences the adoption of two specific policies relevant to HIV risk for YMSM-prescription drug monitoring database programs and parental notification of minors' HIV testing. This research will provide critical formative data that will be used to develop a NIDA R01 proposal that will examine the etiologic pathways through which state-level policies affect HIV risk behaviors for YMSM. The new skills acquired through this K01 will help me achieve my career goal to become an independent investigator who conducts innovative, high impact research examining how and why state-level factors affect substance use and sexual risk behaviors for YMSM with a goal of informing structural-level HIV interventions. This training will position me as one of the few mult-methods researchers working in the policy domain of HIV prevention and enable me to uniquely contribute to the Department of Sociomedical Sciences at Columbia University.